Cyclohexylbenzene is a product of increasing importance in the chemical industry since it offers an alternative route to the Hock process for the production of phenol. The Hock process is a three-step process in which benzene is alkylated with propylene to produce cumene, the cumene is oxidized to the corresponding hydroperoxide and then the hydroperoxide is cleaved to produce equimolar amounts of phenol and acetone. However, the world demand for phenol is growing more rapidly than that for acetone. Thus, a process that uses higher alkenes instead of propylene as feed and coproduces higher ketones, rather than acetone, may be an attractive alternative route to the production of phenols.
For example, oxidation of cyclohexylbenzene has a potential as an alternative route for the production of phenol since it co-produces cyclohexanone, which has a growing market and is used as an industrial solvent, as an activator in oxidation reactions and in the production of adipic acid, cyclohexanone resins, cyclohexanone oxime, caprolactam and nylon 6. However, this alternative route requires the development of a commercially viable process for producing the cyclohexylbenzene precursor.
It has been known for many years that cyclohexylbenzene can be produced from benzene either directly by alkylation with cyclohexene or by the process of hydroalkylation or reductive alkylation. In the latter process, benzene is heated with hydrogen in the presence of a catalyst such that the benzene undergoes partial hydrogenation to produce cyclohexene which then alkylates the benzene starting material. Thus, U.S. Pat. Nos. 4,094,918 and 4,177,165 disclose hydroalkylation of aromatic hydrocarbons over catalysts which comprise nickel- and rare earth-treated zeolites and a palladium promoter. Similarly, U.S. Pat. Nos. 4,122,125 and 4,206,082 disclose the use of ruthenium and nickel compounds supported on rare earth-treated zeolites as aromatic hydroalkylation catalysts. The zeolites employed in these prior art processes are zeolites X and Y. In addition, U.S. Pat. No. 5,053,571 proposes the use of ruthenium and nickel supported on zeolite beta as the aromatic hydroalkylation catalyst. However, these earlier proposals for the hydroalkylation of benzene suffered from the problems that the selectivity to cyclohexylbenzene was low particularly at economically viable benzene conversion rates and that large quantities of unwanted by-products were produced.
More recently, U.S. Pat. No. 6,037,513 has disclosed that cyclohexylbenzene selectivity in the hydroalkylation of benzene can be improved by contacting the benzene and hydrogen with a bifunctional catalyst comprising at least one hydrogenation metal and a molecular sieve of the MCM-22 family. The hydrogenation metal is preferably selected from palladium, ruthenium, nickel, cobalt and mixtures thereof and the contacting step is conducted at a temperature of about 50 to 350° C., a pressure of about 100 to 7000 kPa, a benzene to hydrogen molar ratio of about 0.01 to 100 and a WHSV of about 0.01 to 100. The '513 patent discloses that the resultant cyclohexylbenzene can then be oxidized to the corresponding hydroperoxide and the peroxide decomposed to the desired phenol and cyclohexanone.
However, although the use of MCM-22 family catalysts has allowed a significant increase in product selectivity, the manufacture of cyclohexylbenzene both by direct alkylation and by benzene hydroalkylation still tends to be accompanied by the co-production of significant amounts of by-products. Some of these by-products, such as cyclohexane and dicyclohexylbenzene, can be readily removed from the cyclohexylbenzene product by distillation. However, certain non-fused bicyclic by-products, such as 1,1-methylcyclopentylbenzene and bicyclohexane, have boiling points too similar to that of cyclohexylbenzene to allow their separation by simple distillation. If not removed, these non-fused bicyclic by-products can build up in, and cause problems with, later stages of the phenol production process. Thus, there is interest in developing processes for removing these non-fused bicyclic by-products from the cyclohexylbenzene product.
According to the invention, it has now been found that non-fused bicyclic by-products in cyclohexylbenzene, and other cycloalkylaromatic products of the alkylation of aromatic compounds with cyclic olefins, can be at least partly removed by treating the non-fused bicyclic by-products with a catalyst, especially an acid catalyst, such as faujasite, either alone or in the presence of benzene.